In his introduction to the English version of I Chingmade by one of his acquaintance, Jung admits having

Pa-kua, the eight trigrams which form the basis of I Ching.

practiced the oracle 30 years before meeting Richard Wilhelm, the German translator of the book. Jung was interested in the method of exploration of
the unconscious. He said:

For more than thirty years I have interested myself in this oracle technique, or method of exploring the unconscious, for it has seemed to me of uncommon significance. I
was already fairly familiar with the I Ching when I first met Wilhelm in the early nineteen twenties; he confirmed for me then what I already knew, and taught me many things more. (Foreword to the I Ching)
.

Using the oracle with his patients in psychotherapy Jung could remember a great deal of meaningful answers. He recalled the story of a patient stuck between
ambivalent feelings related to a girl he wanted to ask out (actually the patient suffered from a mother complex). The response of I Ching was hexagram # 44, entitled Coming to Meet, which worn saying:

One should not marry such a maiden.

Fu Hsi is the creator of the pa-kua (eight trigrams). He is depicted as a head sitting on a mountain showing the trigram chart

But how this book manages to give us such inspired answers, asked himself Jung? And he answered: ...A certain curious principle that I
have termed synchronicity, a concept that formulates a point of view diametrically opposed to that of causality. Since the latter is a merely statistical truth and not absolute, it is
a sort of working hypothesis of how events evolve one out of another, whereas synchronicity takes the coincidence of events in space and time as meaning something more than mere chance.

This principle matches the curious mode of functioning of the ancient Chinese mind. Again Jung:

The Chinese mind, as I see it at work in the I Ching, seems to be exclusively preoccupied with the chance aspect of events. What we call
coincidence seems to be the chief concern of this peculiar mind, and what we worship as causality passes almost unnoticed.

In other words: ...Whoever invented the I Ching was convinced that the hexagram worked out in a certain moment coincided with the latter in quality
no less than in time. To him the hexagram was the exponent of the moment in which it was cast.

Psyche and matter are not separated in fact, nor are the inner and outer worlds. In concordance with the

synchronicity principle, the psychic events and those
happening in the outside world may have an acausal, almost simultaneous appearance, a so-called coincidence, and this is way one can use even the ancient method of consulting the oracle to cure neurosis.

Finally: The ancient Chinese mind contemplates the cosmos in a way comparable to that of the modern physicist, who cannot deny that his model
of the world is a decidedly psychophysical structure. The microphysical event includes the observer just as much as the reality underlying the I Ching
comprises subjective, i.e., psychic conditions in the totality of the momentary situation.

As for the practice of I Ching, Jung offers a sample on how to handle the oracle, in
his substantial introduction to the book. You may download his introductory study from